The present invention relates to a flow measuring chamber assembly using an ultrasonic measuring arrangement for determination of a differential flow rate, such assembly being particularly useful for measuring fuel consumption in motor vehicles having a fuel return line.
There is a need in the operation of motor vehicles to determine the rate of fuel consumption. In order to measure fuel consumption, turbine flow meters are conventionally installed in fuel flow lines, these meters being magnetically or optically sensed to provide fuel flow rate determinations. Ultrasonic processes for monitoring fuel flow rates in order to measure fuel consumption have also been proposed. At the present time, difficulties occur in application of known measuring arrangements for determining fuel consumption in cases where the internal combustion engine for a motor vehicle includes a fuel return line disposed in front of the carburetor. In these cases, the rate of fuel consumption is formed as the difference between the forward flow and return flow of fuel. Typically, two separate flow indicators are installed in the forward flow and return flow lines and an electronic device is used to establish the differential flow measurement, such as discussed in "Neuartiger Turbo-Sensor Misst Benzinverbrach", in Vol. No. 24 "Elektronik" (1979), p. 24. A disadvantage in this conventional arrangement, apart from the relatively high manufacturing costs for the installation of two separate flow indicators, is that errors in measurement occur in both instances of the forward and return flow rates. The acummulative effect of these measurement errors leads to high error factors in the differential flow measurement, particularly when small consumption values occur when the differential flow measurement is the difference of two nearly identical magnitudes.
An object of the present invention is to provide a reliable and low-maintenance measuring arrangement which requires low outlay in terms of cost and space requirements and in which there are no accummulative errors in arriving at a differential flow measurement.